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The working principle of the valve positioner

Update:09-07-2019
Summary:

The valve positioner is the main accessory for the regu […]

The valve positioner is the main accessory for the regulating valve and is usually used with pneumatic valves.

Its function is: accept the output signal of the regulator, and then use its output signal to control the pneumatic valve. When the valve is actuated, the displacement of the valve stem is fed back to the valve positioner through the mechanical device, and the valve position is transmitted to the valve position through the electrical signal. Upper system.

The working principle of the valve positioner: the valve positioner can increase the output power of the regulating valve, reduce the transmission hysteresis of the adjustment signal, speed up the movement speed of the valve stem, improve the linearity of the valve, overcome the friction of the valve stem and eliminate The effect of the imbalance force ensures the correct positioning of the regulating valve.

The valve positioner is the main accessory of the control valve. It uses the valve stem displacement signal as the input feedback measurement signal, and uses the controller output signal as the setting signal for comparison. When there is a deviation between the two, the output is changed to the output of the actuator. The signal causes the actuator to act, establishing a one-to-one correspondence between the stem displacement and the controller output signal. Therefore, the valve positioner constitutes a feedback control system in which the valve stem displacement is a measurement signal and the controller outputs a set signal. The manipulated variable of the control system is the output signal of the valve positioner to the actuator.

Valve positioner classification: Generally can be divided into pneumatic valve positioner, electric valve positioner and intelligent valve positioner.

1. Pneumatic valve positioner: A conversion device that converts electrical signals into pressure signals, and uses a compressed air or nitrogen as the working gas source to control the valve position of the valve.

2. Electric valve positioner: Convert the DC current signal given by the control system into the air signal that drives the regulating valve to control the action of the regulating valve. At the same time, feedback is made according to the opening degree of the regulating valve, so that the valve position can be correctly positioned according to the control signal outputted by the system.

3. Intelligent valve positioner: A valve positioner that can automatically detect the zero point, full stroke, friction coefficient of the control valve and automatically set the control parameters without manual adjustment.

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